The objectives of the proposed research are to extend the previous work on Na, Mg, K, HCO3 and Li transport in the cat choroid plexus to include Ca and Li. Then a study of the relation between the transport system responsible for CSF secretion by the choroid plexus and the regulatory systems responsible for maintaining the unique CSF concentration of the ions listed above will be done. This will include a study of the pharmacological characteristics of each system to ascertain whether CSF production can be altered without interfering with ion regulation and vice versa. Next the relation between the transport of various ions by the choroid plexus and the ATPases in that tissue will be studied. Mg dependent and Na-K dependent ATPases have been reported in that tissue and a study will be undertaken to ascertain whether Ca and HCO3/Cl dependent ATPases are present. Subsequently the effects of drugs on the function of the transport systems will be correlated with their effects on these enzyme systems. A study of the role of several endogenous substances (that have been reported to affect CSF) in regulating choroid plexus function will be studied, namely, glucocorticoids, prostaglandins (PGE1), cyclic AMP and GMP and ADH. The major methods will include the isolated choroid plexus in a chamber in situ preparation and hemodialysis. These methods permit one to control, over a wide range, the ion composition and drug levels in the fluid surrounding the choroid plexus and also those in the plasma. The information obtained should provide for a better understanding of CSF physiology and permit more appropriate therapy of CNS disorders and toxicities.